(a) Field of the Invention: capable of forming thermosetting resins having excellent impact resistance and flexibility and low water absorption.
(b) Description of the Related Art:
Thermosetting resins having an imide structure have been used widely in the industry for many years because they have excellent electrical insulating properties and heat resistance and can provide molded or otherwise formed products having superb dimensional stability.
Thermosetting resins obtained from aromatic bismaleimides are however accompanied by the drawbacks of poor impact resistance and toughness, although they are insoluble and infusible and have excellent heat resistance.
As a method for improving the impact resistance and toughness of thermosetting resins obtained from aromatic bismaleimides, it was attempted to use an aromatic diamine along with an aromatic bismaleimide (see U.S. Pat. No. 4,831,102). For example, there was provided a polyaminobismaleimide resin formed from N,N'-(4,4'-methylenediphenylene)bismaleimide and 4,4'-diaminodiphenylmethane. It was however still unsatisfactory in impact resistance and toughness. Further, due to the use of the amine component, there were additional problems such as coloration by the remaining amino groups upon molding or formation and high water absorption of molded or otherwise formed products. In particular, the high water absorption caused internal cracks in molded or otherwise formed products in high-temperature environments. There has hence been a strong demand for the provision of a composition which can achieve a thermosetting resin having low water absorption.
There have also been known a process for producing a crosslinked imido-containing polymer by reacting an aromatic bismaleimide compound, which is different from those useful in the practice of the present invention, with an alkenyl phenol or an alkenyl phenol ether (U.S. Pat. No. 4,100,140) and a thermosetting resin composition obtained by the reaction of 4,4'-bismaleimidediphenylmethane and diallylbisphenol A [see "The 29th National SAMPE Symposium", 392 (1984)]. However, the former was inferior in flexural strength while improvements in strength and toughness characteristics were desired for the latter.